1. Field of the Invention
The invention relates in general to a servo system of an optical disk drive, and more particularly to a method for obtaining an optimum focusing point of an optical pickup unit and a servo system of an optical disk drive using this method.
2. Description of the Related Art
FIG. 1 is a block diagram showing a conventional servo system of an optical disk drive. An optical sensor 102 receives an optical signal reflected from an optical disk 122, and then converts the reflected optical signal into an electric signal before delivering to a pre-amplifier 104 to derive required tracking error signal Te/focusing error signal Fe. The tracking error signal Te/focusing error signal Fe is directed to a compensator 108, which compensates for the gain and phase thereof, and then an optical pickup control signal Foo is obtained. An optical pickup drive circuit 114 receives the optical pickup control signal Foo and generates a control signal T/F used for controlling the position of the optical pickup unit 116. The laser diode (not shown) in the optical pickup unit 116 generates a laser light beam projecting onto the disk 122 during disk-read/write operations.
FIG. 2 shows an exemplary level curve of a focusing error signal Fe with respect to the brightness emitted from the optical pickup unit 116 used for read/write a blank optical disk in the conventional optical disk drive. Assume that the optical pickup unit 116 is positioned at the P point with the Fe signal level at A after related focusing procedure for the optical pickup unit is completed. In this case, the brightness projected onto the blank optical disk is L1, which is usually deviated from the maximum brightness L2 (and the optical pickup unit should be positioned at point Q). Obviously, disk-read/write operations may perform and operate quite well when the optical pickup unit is positioned at the optimum focusing point Q. There is a need to design a servo system of an optical disk drive for finding the optimum focusing point Q such that the optical pickup unit may be moved to this optimum focusing point so as to facilitate the subsequent reading/recording operation on a blank optical disk.